Nitrogen doped graphene was synthesized from graphite oxide and urea by thermal solid-state reaction. The samples were characterized by transmission electron microscopy, atomic force microscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectra, element analysis, and electrical conductivity measurement. The results reveal that there is a gradual thermal transformation of nitrogen bonding configurations from amide form nitrogen to pyrrolic, then to pyridinic, and finally to "graphitic" nitrogen in graphene sheets with increasing annealing temperature from 200 to 700 degrees C. The products prepared at 600 degrees C and 700 degrees C show that the quantity of nitrogen incorporated into graphene lattice is similar to 10 at.% with simultaneous reduction of graphite oxide. Oxygen-containing functional groups in graphite oxide are responsible for the doping reaction to produce nitrogen doped graphene. (C) 2011 Elsevier B. V. All rights reserved.